Add a reference to benchmarks in the README.md

Author: rybakit

README.md

@@ -29,6 +29,7 @@ A pure PHP client for [Tarantool](http://tarantool.io) 1.7.1 or above.
    * [SQL protocol](#sql-protocol)
    * [User defined types](#user-defined-types) 
  * [Tests](#tests)
+ * [Benchmarks](#benchmarks)
  * [License](#license)
 
 
@@ -650,6 +651,11 @@ docker run --rm --net=tarantool-php -v $(pwd):/client -w /client client
 ```
 
 
+## Benchmarks
+
+The benchmarks can be found in the [dedicated repository](https://github.com/tarantool-php/benchmarks).
+
+
 ## License
 
 The library is released under the MIT License. See the bundled [LICENSE](LICENSE) file for details.